CAIRO — Egyptian authorities on Wednesday said they had arrested a leading member of the extremist group al-Qaeda who is wanted by the FBI in connection with the 1998 bombings of U.S. embassies in eastern Africa.

But outside experts and officials in the United States quickly cast doubt on whether Egypt had the right man.

The person arrested was Egyptian-born Mohammed Ibrahim Makkawi, who authorities identified as the senior al-Qaeda leader known as Saif al-Adel (the “sword of justice” in Arabic). Makkawi was arrested at Cairo International Airport, where he was traveling on an Emirates Airline flight from Pakistan via Dubai, airport officials said.

A lawyer who represents clients from jihadist groups denied that Makkawi was Adel. University of Exeter professor Omar Ashour, an expert on Islamist movements, also said that Makkawi and Adel are not the same person.

Ashour said Adel is an Egyptian named Mohamed Salah al-Din Zaidan. Both he and Makkawi served as officers in the Egyptian army, Ashour said, but they have different places of birth and different connections to al-Qaeda.

Saif al-Adel, who the U.S. government says is pictured in this photo, is thought to be affiliated with the Egyptian Islamic Jihad and is believed to be a high-ranking member of the al-Qaeda organization. After Egyptian authorities said he was arrested, outside experts — and officials in the United States — quickly cast doubt on whether Egypt had the right man. (FBI)

Ashour, the University of Exeter professor, said that the picture identified as Adel that is published on the United States’s “most wanted” list shows Zaidan, not Makkawi.

Makkawi, a former Egyptian military officer, was dishonorably discharged for joining jihadist fighters in the 1980s, the lawyer, Nizar Ghorab, said. He was arrested and imprisoned by Egyptian authorities but later fled to Afghanistan. For a very short time he was connected to al-Qaeda, Ghorab said, but he severed his ties years ago.

Ghorab said he expected Makkawi, who had traveled to Egypt from Pakistan via Dubai, to be released within hours.

Security officials in Cairo said Makkawi denied being Adel during questioning and told his interrogators that he split with al-Qaeda over what he felt was bad planning on the organization’s part. He was still being questioned as of 4 p.m. Wednesday (9 a.m. in Washington).

Adel is on the FBI’s most-wanted list for the bombings of the U.S. embassies in Dar es Salaam, Tanzania, and Nairobi 14 years ago. The FBI has offered a $5 million reward for his arrest.

Adel — who in recent years was believed to be living in Iran under house arrest — was briefly Osama bin Laden’s security chief, overseeing al-Qaeda’s military operations. He remains a senior member of the organization and was considered a chief rival of Ayman al-Zawahiri, who took over as commander of al-Qaeda after bin Laden was killed by U.S. Navy SEALs in a raid in 2011.

U.S. officials, who declined to be named because of the sensitivity of the issue, said they don’t believe Makkawi is a high-ranking al-Qaeda figure but added that they are still examining the case.

The State Department’s “Rewards for Justice” program lists Adel’s real name as Ibrahim al-Madani. But a public service announcement that the U.S. government put out seeking information on Adel said he was known as both Ibrahim al-Madani and as Mohammed Ibrahim Makkawi.

A senior Pakistani security official said he could not confirm reports that the person arrested at the Cairo airport had departed from Pakistan, because its agencies were awaiting more information.

“We can’t say that he was on a flight from Pakistan,” said the official, who declined to be identified. “We have no means of confirming that he fled from here until such time as destination officials confirm, verify or negate where he was coming from. We are not really sure. He could have left from Pakistan or Afghanistan or Iran.”

Staff writers Karen DeYoung in Washington and Richard Leiby in Islamabad contributed to this report.